.38-200

.38/200
A box of WWII-dated .380" Revolver Mk IIz cartridges (and separate cartridges)
Type	Revolver
Place of origin	United Kingdom
Service history
In service	United Kingdom (1922–1963)  India (current)
Wars	World War II
Production history
Designer	British Military
Designed	1922
Manufacturer	?
Variants	MkI, MkII
Specifications
Bullet diameter	.361 in (9.2 mm)
Neck diameter	.3855 in (9.79 mm)
Base diameter	.3865 in (9.82 mm)
Rim diameter	.440 in (11.2 mm)
Rim thickness	.055 in (1.4 mm)
Case length	.775 in (19.7 mm)
Overall length	1.240 in (31.5 mm)
Ballistic performance
Bullet mass/type Velocity Energy 200 gr (13 g) LRN 620 ft/s (190 m/s) 176 ft·lbf (239 J)

The .38/200 (or 9×20mmR) was a British military revolver cartridge identical to Smith & Wesson's .38 S&W cartridge but with specific loadings for military service.

The .38 S&W was modified for use by the British military and called the .38/200 (also known as 380/200 Revolver Mk I) in 1922 for .38 caliber pistols and revolvers (such as the Enfield No. 2 Mk I and Webley Mk IV) which replaced the larger .455 and .476 inch handguns. The .38/200 cartridge was initially issued to British military forces as the .380/200 Revolver Mk I round. British authorities later issued a different .38 S&W military cartridge with a lighter, 178–180-grain (12 g) jacketed bullet, known as the .380 Revolver Mk IIz.

After the First World War, there was a move away from the larger .455 calibre. The professional core of the pre-war British Army had been decimated and replaced by a larger and mostly conscripted force. It was recognized that the short training period available to the new recruits did not give them time to become proficient with the large-bore .455 revolvers, and that a smaller caliber would be easier for new recruits to develop competence with in pistol shooting.

British Army initial specifications submitted to ammunition manufacturers for the .38/200 military loading were as follows:

Webley demonstrated a lighter version of their Mk III revolver with modified .38 S&W ammunition, firing a heavy 200-grain (13 g) bullet, later known as the 380/200. It received favorable reports from the Army and the revolver was accepted in principle.

As Webley had used the .38 S&W cartridge dimensions for their revolver, and the cartridge length was fixed by the size of the cylinder of the revolver (the same as for the wider .455), Kynoch produced a cartridge with the same dimensions as the .38 S&W but with 2.8 grains (0.18 g) of "Neonite" nitrocellulose powder and a 200 grain (13.0 g) bullet. This combination gave a velocity of 630 ft/s (189 m/s) at the muzzle, and over 570 feet (170 m) per second at 50 yards (46 m). In tests performed on cadavers and live animals, it was found that the lead bullet, being overly long and heavy for its calibre, become unstable after penetrating the target, somewhat increasing target effect. The relatively low velocity allowed all of the energy of the cartridge to be spent inside the human target, rather than penetrating completely. This was deemed satisfactory and the design for the .38/200 cartridge was accepted as the "380/200 Cartridge, Revolver Mk I".